1. Field of the Invention
The present invention relates to a time base control system in the case where information, such as a video signal an audio signal or the like, is recorded onto or reproduced from a recording medium, such as a disk, a magnetic tape or the like.
2. Background of the Art
For example, one type of time base control systems employed in video disk players has the double function of rough tuning and fine tuning of a time base. The rough tuning is made by controlling the rotational speed of a spindle motor for rotationally driving a recording disk so as to control the relative speed between the recording disk and an information-detection point of a pickup acting as a signal recording/reproducing means. The fine tuning of the time base is made by feeding the reproduced signal obtained by the pickup to a variable delay device such as a CCD (charge coupled device).
In order to reduce the generation of heat and the consumption of electric power of the spindle motor in this type of video disk player, there has been proposed a technique in which the rotation control is made only by a forward driving signal during the time of play or still-reproduction where the revolution speed need not be rapidly changed. On the other hand the rotation control is made by both forward and reverse driving signals during the time of scanning or search where the revolution speed must be rapidly changed.
In such an arrangement, however, the loop gain of the spindle servo for controlling the revolution speed of the spindle motor at the start of scanning or searching is changed so rapidly that the revolution speed of the spindle motor is instantaneously disturbed to permit the disturbance to enter into a CCD loop provided for fine tuning of the time base. Consequently, the problem in the prior art is in that the time base error exceeds the changeable range of signal delay time of the CCD to produce chromatic disorder.